1. Field of the Invention
The invention relates to a video signal enhancement unit comprising:
a pixel counter for generating a count of pixels representative of the number of pixels that occur within a predetermined period of time and which have video signal levels that are higher than a predetermined video level, and
a processing unit for modifying contrast of the video signal in dependence on the count of pixels.
The invention further relates to an image display apparatus provided with:
receiving means for receiving a video signal;
a display device for displaying images represented by the video signal; and
a video signal enhancement unit comprising:
a pixel counter for generating a count of pixels representative of the number of pixels that occur within a predetermined period of time and which have video signal levels that are higher than a predetermined video level, and
a processing unit for modifying contrast of the video signal in dependence on the pixel count.
The invention further relates to a method of video signal enhancement comprising:
generating a count of pixels representative of the number of pixels that occur within a predetermined period of time and which have video signal levels that are higher than a predetermined video level; and
modifying contrast of the video signal in dependence on the count of pixels.
2. Description of the Related Art
A unit of the kind described in the opening paragraph is known from U.S. Pat. No. 5,422,680.
In this unit, the amplitude range of the picture signal can be divided into a number of histogram segments, whereafter, it is determined, by means of a measurement per histogram segment, how often a pixel value, or how long the picture signal, occurs with an amplitude in the relevant histogram segment. Subsequently, the picture signal is processed by a non-linear unit having a transfer characteristic based on the integral of the histogram, i.e., per histogram segment, the picture signal is amplified by a factor which depends on the contents of the relevant measured histogram segment.
A drawback of the unit is that it requires relatively many elements per histogram segment, i.e., pixels, in order to determine an accurate transfer characteristic. This results in a delay of at least one field. Other disadvantages of this unit are its complexity and its costs. Analyzing the video signal, storing several intermediate results, i.e., a histogram, and calculating a transfer characteristic based on the histogram, requires relatively many components.